1. Field of the Invention
The present invention relates to processes for making shelf stable milk beverages.
2. Description of the Related Art
For millennia man has tried unsuccessfully to devise a method for preserving milk which would retain the nutrients and qualities of flesh milk. Roman soldiers subsisted on rations made from dried milk using primitive sun drying techniques. Later technology developed by Gail Borden (1858) resulted in sweetened condensed milk which could be preserved for years using simple concentration methods utilizing water activity as the microbiological control point. More modern milk processing and packaging technologies combine Ultra-High Temperature Processing with aseptic packaging to preserve the shelf-life of milk. The foregoing technologies achieved the preservation aspects but failed to preserve the fresh quality needed for ready to drink products. Sweetened condensed milk is made by concentrating milk 2.5× with added sucrose to control the water activity (α<0.85). Water activity is a measure of food dryness. aw=p/p0, where aw is water activity, p is the vapor pressure of water in the substance, and p0 the vapor pressure of pure water at the same temperature. Water activity as a value has no dimensions. Pure water has a water activity of 1. The resulting product is tan in appearance, has a distinct fat off-taste, coarse texture from lactose crystallization and cannot be reconstituted to a single strength beverage. Similarly, evaporated milk is a 2.1× concentrate which is placed in a can and thermally treated to produce a commercially sterile product (in compliance with 21CFR113). The resulting milk is tan in appearance and unacceptable when diluted to single strength.
Fluid single-strength milk requires a thermal treatment to control microbial growth, inactivate enzymes and stabilize the milk. The Pasteurized Milk Ordinance requires specific time-temperature combinations for the inactivation of infectious pathogens such as Coxiell burnetti, Mycobacterium tuberculosis and Salmonella spp. in refrigerated milk products. Shelf-stable, UHT milk products require a thermal treatment which addresses not only the infectious pathogens but also the toxin producing, heat-resistant spore-formers like Clostridium botulinum or Bacillus cereus. Typical processes fir UHT milk require heating the milk to 286° F. for 6 seconds (or the equivalent process). UHT milk has a pronounced cooked taste and is not well accepted.
UHT/aseptic treatment of milk concentrates has been demonstrated commercially but is technically very difficult due to problems associated with the stability of the concentrated product. Lactose precipitation results in a graininess of the product and slows reconstitution. Hydrolysis of the milk sugar prior to UHT treatment results in increased Maillard reaction browning with noticeable changes in the color and flavor of the milk. Hydrolysis prior to UHT also results in decreased shelf-life for the product.
Hydrolysis of lactose prior to processing results in significant increases in Maillard browning reaction products and produces an unacceptable product. Dosing of lactase enzyme using sterile filtration significantly reduces the browning and extends the life of the product.
The prior art discloses ultra-high pasteurization of milk such as disclosed in Reaves et al., U.S. Pat. No. 6,887,505, for Ultra-High Temperature Pasteurized Milk Concentrate, Package, Dispenser And Method Of Producing Same.
There is a need for a milk concentrate that upon rehydration tastes fresh.